Introduction of the Internet to the general public and the exponential increase in its use has focused attention on high speed backbone networks and switches capable of delivering large volumes of data at very high rates. In addition to the demand for higher transfer rates, many service applications are being developed, or are contemplated, which require guaranteed grade of service and data delivery at guaranteed quality of service. To date, efforts to grow the capacity of the Internet have largely been focused on expanding the capacity and improving the performance of legacy network structures and protocols. Many of the legacy network structures are, however, difficult to scale into very high-capacity networks. In addition, many legacy network protocols do not provide grade of service or quality of service guarantees.
Nonetheless, high capacity switches are known in the prior art. Prior art high capacity switches are commonly constructed as a multi-stage, usually three stage, architecture in which ingress modules communicate with egress modules through a switch core stage. The transfer of data from the ingress modules to the egress modules must be carefully coordinated to prevent contention and to maximize the throughput of the switch. Within the switch, the control may be distributed or centralized. A centralized controller must receive traffic state information from each of the ingress modules. Each ingress module reports the volume of waiting traffic destined to each of the egress modules. The centralized controller therefore receives traffic information related to traffic volume from each of the ingress modules. If, in addition, the controller is made aware of the class of service distinctions among the waiting traffic, the amount of traffic information increases proportionately. Increasing the amount of traffic information increases the number of control variables and results in increasing the computational effort required to allocate the ingress/egress capacity and to schedule its usage. Consequently, it is desirable to keep the centralized controller unaware of the class of service distinctions while providing a means of taking the class of service distinctions into account during the ingress/egress transfer control process.
This is accomplished in a rate-controlled multi-class high-capacity packet switch described in Applicant's copending U.S. patent application Ser. No. 09/244,824 which was filed on Feb. 4, 1999. Although the switch described in this patent application is adapted to switch variable sized packets at very high speeds while providing grade-of-service and quality-of-service control, there still exists a need for a distributed switch that can form the core of a powerful high-capacity, high-performance network that is adapted to provide wide geographical coverage with end-to-end capacity that scales to hundreds of Tera bits per second (Tbs), while providing grade of service and quality of service controls.
A further challenge in providing a powerful high-capacity: high-performance switch with wide geographical coverage is maintaining network efficiency in the face of constantly fluctuating traffic volumes. In response to this challenge, the Applicant also invented a self-configuring data switch comprising a number of electronic switching modules interconnected by a single-stage channel switch that includes a number parallel space switches, each having input ports and output ports. This switch architecture is described in Applicant's copending United States patent application entitled SELF-CONFIGURING DISTRIBUTED SWITCH which was filed on Apr. 6, 1999 and assigned application Ser. No. 09/286,431. Each of the electronic modules is capable of switching variable-sized packets and is connected to the set of parallel space switches by a number of optical channels, each of the optical channels being a single wavelength in a multiple wavelength fiber link. The channel switching core permits any two modules to be connected by an integer number of channels. In order to enable the switching of traffic at arbitrary transfer rates, the inter-module connection pattern is changed in response to fluctuations in data traffic load. However, given the speed of optical switching equipment and the granularity of the channels, it is not always possible to adaptively modify the paths between modules to accommodate all data traffic variations. Consequently, it sometimes proves uneconomical to establish under-utilized paths for node pairs with low traffic volumes. To overcome this difficulty, a portion of the data traffic flowing between a source module and a sink module is switched through one or more intermediate nodes. Thus, in effect, the switch functions as a hybrid of a channel switch and linked buffer data switch, benefiting from the elastic path capacity of the channel switch.
A concentration of switching capacity in one location is, however, undesirable for reasons of security and economics. Consequently, it is desirable to provide a high-capacity switch with a distributed core. Such a core has the advantages of being less vulnerable to destruction in the event of a natural disaster, for example. It is also more economical because strategic placement of distributed core modules reduces link lengths and provides shorter paths for localized data traffic.
There therefore exists a need for a very high-capacity packet switch with a distributed core that is adapted to provide grade of service and quality of service guarantees. There also exists a need for a very high-capacity packet switch that provides intra-switch data paths of a finer granularity to reduce or eliminate a requirement for tandem switching.